The present invention relates to a method and apparatus for color marking insulated electrical conductors. The method and arrangement for marking insulated electrical conductors includes a stream of color material continuously emerging under pressure from a spray nozzle disposed at a right angle to the electrical conductor and is caused to oscillate by a deflection system subjected to a high alternating voltage. The deflection voltage for the stream of color material ensures that the color ring marks are produced at all marking frequencies coming into question.
Such arrangements for color marking insulated electrical conductors are known and have proved good in practice. In the known marking apparatus, the deflection system is subjected to a sinusoidal alternating voltage. This results in a sinusoidal deflection of the stream of color material, which produces, in a known manner, a half ring on the longitudinally advancing extruded insulated electrical conductor at the zero crossing of the sinusoidal oscillation. The production of two ring marks composed of two separately produced half rings functions excellently for a wide range of ring spacings and extruder take-off speeds. Difficulties may be encountered only with very large ring spacings, which correspond to low frequencies of the deflection voltage, and/or at high extruder take-off speeds for the following reason.
To be able to produce the whole spectrum of ring marks at the high extruder take-off speeds of modern extruders insulating the electrical conductor, streams of color material are needed which are deflected at frequencies between about 200 and 2,000 Hz (hertz). At a constant pressure of the color material, the number of wave trains of the deflected color stream between the point of origin, i.e. the deflecting electrodes, and the marking plane varies by a factor of 10 also.
When the number of wave trains of the sinusoidally deflected stream of color material is small, i.e., at a low deflection frequency or with a large ring spacing and/or at a high extruder take-off speed, the conductor, while the stream of color material is passing over it, travels a distance which is not negligible. As a result, the ring mark becomes wider, increasingly oblique, and distorted in the form of two half circles. In addition in the known marking apparatus, the amplitudes of the stream oscillations are not generally equal to each other. One of the reasons for this is, for example, that the spray nozzles have different diameters when a small amount of color material has deposited in one of the nozzles. Another reason may be that the color material in the feed pipe to one spray nozzle is given a charge different from that applied in the other feed pipe, and this may result in different deflection properties.